The present invention relates to a process for producing an olefin/styrene/diene type cross-copolymer or cross-copolymerization product having excellent mechanical properties and high heat resistance and being excellent in processability and economical efficiency, and the obtained cross-copolymer or cross-copolymerization product, and further an excellent process for producing an olefin/diene type cross-copolymer or a cross-copolymerization product. Further, it relates to their applications.
Ethylene/styrene Copolymers
Some ethylene/styrene random copolymers obtainable by means of a so-called Ziegler-Natta catalyst system comprising a transition metal catalyst component and an organic aluminum compound, and processes for their production, are known.
JP-A-3-163088 and JP-A-7-53618 disclose ethylene/styrene copolymers containing no normal (i.e. head-to-tail) styrene chain, so-called pseudo-random copolymers, obtainable by means of a complex having a so-called constrained geometric structure.
JP-A-6-49132 and Polymer Preprints, Japan, 42, 2292 (1993) disclose processes for producing similar ethylene/styrene copolymers containing no normal styrene chain, i.e. pseudo-random copolymers, by means of a catalyst comprising a cross-linkeded metallocene type Zr complex and a cocatalyst. These copolymers have no stereoregularity derived from styrene units.
Further, recently, it has been reported to produce an ethylene/styrene copolymer having a stereoregularity of alternating copolymerization type by means of a certain specific cross-linkeded bisindenyl type Zr complex i.e. a racemic [ethylenebis(indenyl)zirconium dichloride] under an extremely low temperature (xe2x88x9225xc2x0 C.) condition. (Macromol. Chem., Rapid Commun., 17, 745 (1996).) However, with the copolymer obtainable by this complex, the molecular weight is not yet practically sufficient, and the compositional distribution is also large.
The above copolymers have no styrene chain structures and thus have drawbacks that the compatibility with styrene type polymers is low, and they are not suitable for use as an alloy or a compatibilizing agent for styrene type polymers. Further, their mechanical properties such as the initial modulus of elasticity and high temperature characteristics (heat resistance) are also inadequate.
Further, JP-A-9-309925 and JP-A-11-130808 disclose novel ethylene/styrene copolymers which respectively have styrene contents of from 1 to 55 mol % and from 1 to 99 mol % and which have ethylene/styrene alternating structures and isotactic stereoregularity in their styrene chain structures and further have head-to-tail styrene chain structures, with the alternating degrees (xcex values in this specification) of the copolymers being at most 70. Further, these copolymers have high transparency. However, even with such ethylene/styrene copolymers, the content of styrene chains is not adequate, and they are not adequate for use as a compatibilizing agent or as a component of an alloy. Further, their mechanical properties such as the initial modulus of elasticity and high temperature characteristics (heat resistance) are not yet fully satisfactory.
Ethylene/xcex1-olefin Copolymers
Ethylene/xcex1-olefin copolymers having 1-hexene, 1-octene or the like co-polymerized to ethylene, i.e. so-called LLDPE, are flexible and transparent and have high strength, whereby they are widely used as e.g. films for general use, packaging materials or containers. However, as a nature of polyolefin type resins, their printability and coating properties are low, and special treatment such as corona treatment will be required for printing or coating. Further, they have poor affinity with an aromatic vinyl compound polymer such as a polystyrene or a polar polymer, and in order to obtain a composition with such a resin having good mechanical properties, it has been necessary to employ an expensive compatibilizing agent additionally. Further, they have also a problem that the surface hardness is low, and they are susceptible to scratching.
Grafted Ethylene/p-methylstyrene Copolymer
On the other hand, an attempt to synthesize a graft product of a p-methylethylene/styrene copolymer with other resin by means of a metallocene catalyst or CGCT catalyst, has been reported, for example, in WO/9616096A1, U.S. Pat. No. 5,543,484 or J. Polym. Sci. PartA, Polym. Chem., 36, 1017 (1998).
Such method is designed so that methyl groups of p-methylstyrene units of the copolymer are activated, e.g. lithio-modified, so that the graft polymerization is carried out using them as polymerization initiation points. However, it is necessary to chemically activate methyl groups after the copolymer is recovered and purified from the polymer solution. Further, to complete this process, a reaction for a long period of time is required, such being not practical. There is an additional problem that p-methylstyrene is expensive as compared with styrene. The graft copolymer thus obtained usually has graft chains independently branched from the polymer main chain, but when it is used as a compatibilizing agent or as a composition, the strength of the interface of the polymer microstructure can not be said to be adequate.
Common Graft Copolymers
As a method for obtaining a graft copolymer, a method has been heretofore known wherein a graft copolymer of an olefin type polymer or an olefin/styrene type copolymer is obtained during the polymerization or during the mold processing by a common known radical graft treatment. However, this method is disadvantageous from the viewpoint of costs. Further, the obtainable graft copolymer usually has a problem that it is non-uniform and partially gelled to be not soluble, whereby the moldability tends to be impaired. The graft copolymer thus obtained, usually has graft chains independently branched from the polymer main chain, but when such copolymer is employed as a composition or a compatibilizing agent, the strength of the interface of the polymer microstructure can not be said to be sufficient.
Grafted Syndiotactic Polystyrene
JP-A-11-124420 discloses a technique for improving toughness of a syndiotactic polystyrene by synthesizing an olefin/styrene/diene copolymer by means of a coordination polymerization catalyst containing a metallocene catalyst, followed by coordination polymerization to graft-copolymerize (cross-copolymerize in this invention) a syndiotactic polystyrene chain. However, there is no other disclosure than the production of a graft-copolymerized syndiotactic polystyrene. Besides, with the disclosed coordination polymerization catalyst, the ability to copolymerize a diene (divinylbenzene) is so low that a large amount of the diene has to be charged to the polymerization solution in the coordination polymerization step, and a large amount of an unreacted diene will consequently remain in the polymerization solution. If such a coordination polymerization solution is used as it is in the subsequent step, the crosslinking degree of the obtainable polymer tends to be extremely high due to the remaining diene, thus leading to gelation or substantial deterioration in the processability. Therefore, it will be required to separate and purify the polymer from the coordination polymerization solution before proceeding with the next graft copolymerization step. The separation and purification of the polymer from the polymer solution are very cumbersome and will bring about a substantial increase of costs.
Cross-copolymerization by Anionic Polymerization
JP-A-1-118510 discloses a technique to synthesize an olefin/divinylbenzene copolymer by coordination polymerization employing a Zieglar-Natta catalyst and then graft (the same meaning as cross-copolymerize in the present invention) polystyrene chains by anionic polymerization. In this technique, a Zieglar-Natta catalyst is employed in the coordination polymerization step, the diene content in the obtained copolymer is highly non-uniform, and accordingly, the copolymer obtainable by grafting is also non-uniform and is likely to undergo gelation or to have poor processability. Further, an aromatic vinyl compound (styrene) is not included in the concept of the olefin/divinylbenzene copolymer in this technique.
Besides, with the disclosed Zieglar-Natta catalyst, the ability to copolymerize a diene (divinylbenzene) is low, whereby a large amount of the diene has to be charged to the polymerization solution in the coordination polymerization step, and a large amount of an unreacted diene will consequently remain in the polymerization solution. If such a coordination polymerization solution is used as it is in the subsequent step, the crosslinking degree of the obtainable polymer will be very high due to the remaining diene, whereby gelation or substantial deterioration of the processability will be brought about. Therefore, separation and purification of the polymer from the coordination polymerization solution are required before proceeding with the next graft copolymerization step. The separation and purification of the polymer from the polymerization solution are very cumbersome and will bring about a substantial increase of the costs.
Likewise, even if a common single site coordination polymerization catalyst (homogeneous type coordination polymerization catalyst) is used as it is, the ability to copolymerize a diene (divinylbenzene) is usually inadequate, and a similar problem will result.
Polystyrene Type Resin Composition
On the other hand, an aromatic vinyl compound type resin such as a styrene type resin or a rubber-reinforced styrene type resin, is a material excellent in dimensional stability and stiffness, but has a drawback that it is inferior in the mechanical property, particularly in toughness. As an aromatic vinyl compound type resin, a rubber-reinforced styrene type resin (HIPS) having an elastic rubber phase dispersed non-continuously in a hard resin, is used for the purpose of improving the impact resistance. The impact resistance increases in correspondence with the rubber material, but the mechanical strength (tensile strength, stiffness), the heat resistance, the moldability, the surface gloss, etc., tend to decrease. Further, there is a drawback that the resin is likely to undergo heat deterioration during molding due to double bonds of butadiene or isoprene of the rubber material. Further, with a composition of a hydrogenated styrene/butadiene block copolymer and a styrene type resin, there is a problem that the stiffness of the resin composition decreases to a large extent. WO98/10014 discloses a composition containing an aromatic vinyl compound type resin employing an ethylene/styrene pseudo-random copolymer obtainable by means of a geometrically constrained catalyst (CGCT catalyst). However, the pseudo-random copolymer contains no chain structure of aromatic vinyl compound units, and the content of the aromatic vinyl compound units is limited to at most 50 mol % at the maximum, whereby it has particularly low compatibility with an aromatic vinyl compound type polymer, and the physical properties of the composition are rather limited.
Apart from the above, JP-A-9-309925 and JP-A-11-130808 disclose high molecular weight ethylene/styrene copolymers which have styrene contents of from 1 to 55 mol % and from 1 to 99 mol %, respectively, and which have an ethylene/styrene alternating structure and a styrene chain structure, wherein the styrene chain structure has an isotactic stereoregularity. However, also in this copolymer, the proportion of the styrene chain structure contained is small in a compositional range where the styrene content is relatively low to have rubber elasticity and flexibility which are useful particularly for a composition, and the compatibility with an aromatic vinyl compound type polymer is not adequately improved.
Polyolefin Composition
Polyolefins such as polyethylene and polypropylene have been typical general purpose plastics and have been used in a large quantity as household products. For example, polyethylene or polypropylene is excellent in mechanical strength, moldability, heat resistance, chemical resistance, etc., and is used in many areas as a general purpose resin for films, containers, etc. Further, in recent years, with an improvement in the polymerization technique of polyolefins, it has become possible to obtain high performance polyolefins, and it has been attempted to use them in the field where engineering plastics used to be employed. However, their impact resistance is not sufficient, and it is difficult to use them for automobile parts such as bumpers or instrument panels or housing parts of household products such as refrigerators and washing machines.
For the purpose of overcoming such a drawback, a method is known to incorporate an olefin type elastomer such as ethylene/isobutene, an ethylene/propylene copolymer (EPR) or an ethylene/1-octene copolymer, to polyolefins. However, a difficulty will result such that the surface hardness tends to decrease, whereby the product is susceptible to scratching. Further, a hydrogenated resin such as SEBS, SIPS has been employed as a modifier for polyolefins, and the impact resistance has been improved. However, such a hydrogenated resin has a drawback that it is expensive.
WO98/10015 and JP-A-10-60194 disclose a composition containing a polyolefin type resin employing an ethylene/styrene pseudo-random copolymer obtainable by means of a geometrically constrained catalyst (CGCT catalyst). For example, a composition of polypropylene and an ethylene/styrene copolymer, shows an effect to improve the impact resistance, but there still remains a room for improvement in the balance with mechanical properties (flexural strength, flexural modulus of elasticity).
Compatibilizing Agent
A polymer composition is desired whereby different properties such as the high stiffness and glass transition temperature of an aromatic vinyl compound type polymer and the flexibility, low glass transition point and high solvent resistance derived from the crystal structure of an olefin type polymer, are well balanced. However, heretofore, the desired physical properties have not been obtained with a composition prepared by blending an aromatic vinyl compound type polymer and an olefin type polymer, since the compatibility between these resins is poor. Therefore, various compatibilizing agents have been studied.
As such compatibilizing agents, hydrogenated block copolymers (SEBS, SEPS, etc.) obtained by hydrogenating block copolymers of e.g. an aromatic vinyl compound and a diene compound, have been employed. (J. Polym. Sci., Polym. Letters, 19, 79 (1981), JP-A-56-38338, U.S. Pat. No. 4,020,025, etc.). These resins are very expensive, since they are produced via a hydrogenation step which is highly costly. Further, the mechanical properties (breaking strength, tensile modulus of elasticity, elongation) etc. of the obtainable compatibilizing compositions are also inadequate.
U.S. Pat. No. 5,460,818 discloses a composition employing an ethylene/styrene pseudo-random copolymer obtained by means of a geometrically constrained catalyst (CGCT catalyst), as a compatibilizing agent for an aromatic vinyl compound type polymer and an olefin type polymer. However, in the pseudo-random copolymer, no chain structure of aromatic vinyl compound units is contained, and the content of aromatic vinyl compound units is limited to at most 50 mol % at the maximum, and in particular, the compatibility with an aromatic vinyl compound type polymer is low, whereby its performance as a compatibilizing agent for the physical properties of the composition are rather limited.
Further, apart from the above, JP-A-9-309925 and JP-A-11-130808 disclose high molecular weight ethylene/styrene copolymers which have styrene contents of from 1 to 55 mol % and from 1 to 99 mol %, respectively, and which have an ethylene/styrene alternating structure and a styrene chain structure, wherein the styrene chain structure has isotactic stereoregularity. However, also in these copolymers, the proportions of styrene chain structures contained are small in the compositional range where the styrene content is relatively low and where they have rubber elasticity and flexibility useful as compatibilizing agents, and no adequate improvement has been made in the compatibility with an aromatic vinyl compound type polymer.
Cross-linkeded Product of a Resin and a Resin Composition
A method for crosslinking by means of a crosslinking agent such as a peroxide or sulfur is known to improve the properties such as the compression set, of an olefin/diene type resin such as an ethylene/propylene/diene copolymer (EPDM), an elastomer, an olefin type resin such as an ethylene/propylene copolymer (EPR) or ethylene/octene, or an elastomer. However, a cross-linkeded product of such an olefin/diene type resin or an olefin type resin has a low polarity, and its compatibility with other resins, the coating property, etc., have been inadequate.
Further, WO96/07681, WO99/10395 and U.S. Pat. No. 5,869,591 disclose mainly cross-linkeded products of ethylene/aromatic vinyl compound pseudo-random copolymers. JP-A-11-293045, JP-A-11-293046 and JP-A-11-293072 disclose dynamic cross-linkeded products of ethylene/aromatic vinyl compound copolymers having aromatic vinyl compound chains and stereoregularity. Further, JP-A-7-278231 and JP-A-10-298242 disclose cross-linkeded products of ethylene/xcex1-olefin/aromatic vinyl compound random copolymers, and JP-A-7-278230, JP-A-8-134140, JP-A-8-225615 and JP-A-10-168242 disclose cross-linkeded products of ethylene/xcex1-olefin/aromatic vinyl compound/non-conjugated diene random copolymers. Further, JP-A-10-264325, JP-A-10-264313 and WO98/31540 disclose cross-linkeded products of ethylene/aromatic vinyl compound/non-conjugated polyene copolymers.
Cross-linkeded products employing such ethylene/aromatic vinyl compound (styrene) copolymers have had a drawback that particularly, the tensile modulus of elasticity, the heat resistance and the cold resistance are low, and no adequate mechanical strength can be obtained. Further, for the three-component type or four-component type copolymers, the polymerization behaviors tend to be complex, whereby reproducibility tends to be inadequate. For an industrial production, a complicated plant will be required, such being not economical.
Further, an ethylene/aromatic vinyl compound (styrene) copolymer itself has a low crosslinkable property. Accordingly, in order to obtain adequate degree of crosslinking, it is necessary to use a large amount of a crosslinking agent, a crosslinking accelerator, a crosslinking accelerating adjuvant and/or a co-crosslinking agent, such being disadvantageous from the viewpoint of costs. Further, it has had a drawback that due to such additives, a bad odor may remain in the product. To overcome such a drawback, if it is attempted to copolymerize a non-conjugated polyene or a non-conjugated diene in the first polymerization step to introduce crosslinking points to an ethylene/aromatic vinyl compound (styrene) copolymer, it will be required to copolymerize a relatively large amount of the diene, whereby the obtained copolymer itself is likely to undergo crosslinking during the polymerization and tends to be in-solubilized or gelled, thus leading to deterioration of the physical properties or processability.
Foamed Products of a Resin and a Resin Composition
Foamed products obtained by foaming thermoplastic resins are excellent in lightweight, heat insulating properties, sound-proofing properties, vibration-absorbing properties, shock-absorbing properties, gas-permeability, etc., and thus they are used as packaging materials such as food containers, shock-absorbing materials, heat-insulating materials, etc. As specific application fields, food-packaging materials, packing materials for e.g. instruments, building materials and construction materials, may, for example, be mentioned.
The thermoplastic resin as a base material for such a foamed product, may, for example, be an olefin type resin such as an ethylene or propylene type resin, a styrene type resin, a urethane type resin or a vinyl chloride type resin.
An olefin type resin such as polyethylene or polypropylene, usually has high crystallinity and undergoes a rapid viscosity change along with melting of the crystal, whereby mold processing is not necessarily easy. For the purpose of improving the melting properties, crosslinking or the like has been carried out. Further, it has been inadequate also with respect to the balance of the mechanical properties and heat resistance of the obtained foam.
An urethane type resin foam has a characteristic such that it is excellent in recovery from compression. However, the urethane bond is readily hydrolysable, whereby there is a problem in the chemical stability. Further, it has a drawback that the cost tends to be expensive for industrial production.
With respect to a PCV foam, with a view to improving the environmental aptitude of the material, there has been an increasing demand for substitution of a polyvinyl chloride type material for other materials, since chlorine or a chlorine type compound is generated during decomposition or incineration and an adverse effect of the contained plasticizer to a living body is feared.
WO99/10395, U.S. Pat. No. 5,869,591, JP-A-11-293023, WO99/47592 and JP-A-9-309925 disclose crosslinked products of ethylene/aromatic vinyl compound/(diene) copolymers (compositions) and their foamed products. Exemplified as Examples, are cross-linkeded products of ethylene/styrene copolymers such as pseudo-random copolymers, and the cross-linkeded structure is a network structure having diene moieties in the polymer main chain connected by a crosslinking agent.
These foamed products composed mainly of ethylene/styrene copolymers have a characteristic that they are superior to a styrene composition in flexibility. However, at a low temperature, such flexibility tends to be lost, and it also has a drawback that the heat resistance is low. Therefore, the low temperature characteristics and the heat resistance are improved by crosslinking or making a composition with a resin such as LLDPE. Even then, no adequate improvement has been attained in the temperature dependency of the soft touch feeling. Further, a foamed product composed mainly of an ethylene/styrene copolymer is excellent as a soft foam since the initial modulus of elasticity is low, but it is not suitable for use in an application to a foam which is required to have a certain degree of stiffness and flexibility at the same time.
The present invention is firstly to provide a novel cross-copolymer which overcomes the above-mentioned drawbacks of conventional ethylene/styrene copolymers and ethylene/xcex1-olefin copolymers and various graft and cross-copolymers heretofore proposed and to provide a novel, efficient and economically excellent process for its production.
The present invention is secondly to provide various resin compositions or processed products containing the cross-copolymer, which have the above-mentioned problems of various conventional resin compositions or processed products solved or improved.
Cross-copolymer (a Cross-copolymer)
The cross-copolymer of the present invention is a cross-copolymer which is a copolymer obtained by cross-copolymerizing (intersectingly copolymerizing) a vinyl compound polymer to an olefin/styrene/diene copolymer having a styrene content of from 0.03 mol % to 96 mol %, a diene content of from 0.001 mol % to 3 mol % and the rest being an olefin (which will be referred to as a cross-copolymerized olefin/styrene/diene copolymer or an olefin/styrene/diene type cross-copolymer in this specification), wherein cross-copolymerized cross chains are other than a syndiotactic aromatic vinyl compound polymer (syndiotactic polystyrene).
Further, the cross-copolymer of the present invention is a copolymer which can be obtained by the following process i.e. by the coordination polymerization step and the crossing step.
Further, the present invention is a cross-copolymer constituted preferably by the structure shown in FIG. 1 or comprising mainly the structure shown in FIG. 1.
Namely, as shown in FIG. 1, it is a copolymer having mainly a structure in which a main chain olefin/styrene/diene copolymer and a vinyl compound polymer are cross-bonded (intersectingly bonded), at one point or plural points of the main chain. Such a cross-bonding structure may be rephrased as a star structure. Further, in the classification by the POLY division of the United States Chemical Society, it is called a segregated star copolymer (Polymer Preprints, 1998, March). The vinyl compound polymer cross-bonded to the main chain olefin/styrene/diene copolymer will be referred to as a cross chain.
Whereas as shown in FIG. 2, a graft copolymer known to those skilled in the art is a copolymer having mainly polymer chains branched from one point or plural points of the main chain.
With a structure such that a polymer main chain is cross-bonded (intersectingly bonded) with other polymer chains (which may be called also as a star structure), it is usually possible to obtain superior strength of the interface of the polymer microstructure as compared with a grafted structure, when it is employed as a composition or a compatibilizing agent, whereby it is believed to present high mechanical properties.
Further, the present invention is an olefin/styrene/diene type cross-copolymerization product excellent in processability, whereby MFR as measured under a load of 5 kg at 200xc2x0 C. is at least 0.05 g/10 min, preferably at least 0.2 g/10 min.
Further, the present invention is a cross-copolymer characterized in that the cross-copolymerized cross chains have substantially no stereoregularity. Namely, it is characterized in that the racemic diad index or meso diad index is less than 0.85, preferably at most 0.75 in an olefin/styrene/diene cross-copolymer.
The present invention is preferably an olefin/styrene/diene type cross-copolymer wherein the olefin is ethylene or at least two olefins including ethylene.
Further, the present invention is more preferably an olefin/styrene/diene type cross-copolymer having an aromatic vinyl compound polymer as cross chains.
The olefin/styrene/diene type cross-copolymer of the present invention is a cross-copolymer obtained by using an olefin/styrene/diene copolymer having a styrene content of from 0.03 mol % to 96 mol %, a diene content of from 0.0001 mol % to 3 mol % and the rest being an olefin.
According to the present invention, a process for producing an olefin/styrene/diene type cross-copolymer or cross-copolymerization product having excellent mechanical properties and high heat resistance and being excellent in processability and economical efficiency, is provided, and the olefin/styrene/diene type cross-copolymer or cross-copolymerization product is provided. Further, an excellent process for producing an olefin/diene type cross-copolymer or cross-copolymerization product is provided. These cross-copolymers and cross-copolymerization products are extremely useful in a wide range of applications.